First slide

Intensity of electromagnetic wave

Question

A point source of electromagnetic radiation has an average power output of 800 W. The maximum value of electric field at a distance of 4.0 m from the source is

Moderate

A

64.7 V/m
B

57.8 V/m
C

56.72 V/m
D

54.77V/m

Solution

The intensity of electromagnetic wave is
$I = \frac{P_{av}}{2 {πr}^{2}} = \frac{E_{0}^{2}}{μ_{0} c} ∴ E_{0} = \sqrt{(\frac{μ_{0} {cP}_{αV}}{2 {πr}^{2}})} = \sqrt{[\frac{(4 π \times 10^{- 7}) \times (3 \times 10^{8}) \times 800}{2 π \times (4)^{2}}]} = 54 \cdot 77 V / m$

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